Blast shield for use in wireless transmission system

ABSTRACT

A blast shield includes a blast resistant housing having a transmission wall which allows transmission of wireless signals therethrough. The shield is especially useful for withstanding external explosions, shock waves and thermal shock such as may occur during the collapse or explosions in underground mines, buildings or other environments while protecting internal components such as wireless transmitters and sensitive electronic equipment. The shield is also configured to prevent electrical arcing or explosions within the housing from escaping the housing and igniting flammable material external to the housing. A wireless transmission system using the blast shield and a method of use are also provided.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to a blast shield for use in wireless transmission. More particularly, the blast shield is configured to house various electronic components such as transmitters so that a wireless signal may be transmitted through a portion of the blast shield. Specifically, the blast shield is typically configured to protect the various components contained therein from external explosions or shock waves while minimizing the possibility of igniting external flammable gasses or other materials in the case of an explosion within the blast shield.

2. Background Information

With the increasing use of wireless mesh networks for communication, controls and data transfer in various industries and applications, there is a need for ruggedized explosion proof enclosures to house various components such as relays, transmitters, antennas and various other types of sensitive electronic equipment. Such enclosures would desirably maximize survivability of the various components in case of catastrophic events such as explosions while also preventing internal explosions from causing secondary explosions external to the enclosure.

BRIEF SUMMARY OF THE INVENTION

The present invention generally provides a blast shield or enclosure in which various electronic components such as wireless transmitters may be disposed for transmitting wireless signals through a portion of the enclosure. The enclosure is typically configured to prevent internal explosions, flames or arcing from exiting the enclosure in order to prevent ignition of external flammable gasses or the like outside the enclosure. The enclosure may also be configured to withstand external explosions or blast waves or the impact of various types of projectiles in order to protect the internal components. The present invention also includes the wireless transmission system and method of using this system.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A preferred embodiment of the invention, illustrated of the best mode in which Applicant contemplates applying the principles, is set forth in the following description and is shown in the drawings and is particularly and distinctly pointed out and set forth in the appended claims.

FIG. 1 is a perspective view of the blast shield of the present invention shown mounted on a wall or other support structure.

FIG. 2 is a top plan view of the base plate of the blast shield.

FIG. 3 is a bottom plan view of the transmission wall of the blast shield.

FIG. 4 is a top plan view of the retaining ring.

FIG. 5 is a perspective view of the housing of the gland seal.

FIG. 6 is a top plan view of the blast shield shown mounted on the support structure with one gland seal assembled and the other gland seal disassembled with the gland seal nut separated from the housing. FIG. 6 further shows in dash lines various internal components within the blast shield.

FIG. 7 is a sectional view taken on line 7-7 of FIG. 6.

FIG. 8 is an enlarged sectional view of the encircled portion of FIG. 7.

FIG. 9 is a sectional view taken on line 9-9 of FIG. 6 illustrating the connection or assembly of the gland seal to provide the seal around the associated cable or wire.

FIG. 9A is a sectional view taken on line 9A-9A if FIG. 6 illustrating the gland seal and the associated fire resistant pathways thereof.

FIG. 10 is similar to FIG. 9 and shows an alternate embodiment of a gland seal.

FIG. 11 is a diagrammatic view showing several of the blast shields within a wireless transmission system.

Similar numbers refer to similar parts throughout the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The blast shield of the present invention is indicated generally at 10 in FIG. 1. Blast shield 10 is shown mounted on a wall or other support structure 12 and is used to house various internal components 14 (shown in dashed lines in FIG. 6) which are part of a wireless transmission system such as shown in FIG. 11. Shield 10 is configured in part to protect internal components 14 from damage which may otherwise be sustained by the impact of solid objects or a blast wave such as may occur during an explosion or, for instance, the collapse of an underground mine or the collapse of another type of structure such as a building or the like. Shield 10 is also configured to prevent internal sparks, flames, explosions or electric arcs within the blast shield from igniting flammable gasses or other materials which may be disposed adjacent and external to shield 10. Shield 10 may be configured to meet various requirements such as those established within various industries or by governmental agencies, such as within the underground mining industry, petrochemical industry, manufacturing industry, and the federal Homeland Security agency.

Before describing the blast shield in greater detail, internal components 14 are briefly described. Components 14 typically include a radio transceiver unit 15, an antenna 17 connected thereto, battery-charging power wires 19 and optionally signal-transmission lines 21. Unit 15 may thus serve as a wireless relay and typically includes a radio frequency receiver and radio frequency transmitter for producing signals which are transmitted wirelessly via antenna 17. Unit 15 further includes a battery which powers the receiver and transmitter and a battery charger for charging the battery via power wires 19. The charger thus typically includes a rectifier for transforming alternating current to direct current. Unit 15 may also include a microprocessor for processing incoming wireless signals and translating them into outgoing signals over transmission lines 21, which may be in the form of fiber optic lines or electric wires for example.

With primary reference to FIG. 1, shield 10 includes a rigid base mounting structure in the form of a flat circular base or base plate 16, a blast-resistant dome shaped transmission wall 18 and a securing mechanism which secures wall 18 to plate 16 and includes a circular retaining ring 20 and multiple fasteners 22. In the exemplary embodiment, there are sixteen fasteners 22 which are circumferentially evenly spaced along ring 20. Shield 10 further includes a pair of gland seals 24A and 24B which are configured to provide a water tight, airtight seal around wires or cables such as flexible electric power cable 26 and flexible signal transmission cable 28, respectively, which extend through holes formed in transmission wall 18 of shield 10. Each of these cables includes an internal electrical conductor or wire with an outer layer of electrical insulation. Power cable 26 is in electrical communication with the internal battery charger via power wires 19 (FIG. 6) when shield 10 is assembled. Cable 28 is likewise in electrical or optical communication with unit 15 via transmission lines 21 so that signals may be transmitted through lines 21 and cable 28 from inside shield 10 to outside shield 10. Although shield 10 may be mounted as shown in FIG. 1 on a generally vertical wall, on a floor, on a ceiling or overhanging structure, or in any other desired position, it will be described herein for simplicity as having a top 30 and a bottom 32 so that plate 16 defines bottom 32 and transition wall 18 is mounted atop plate 16 so as to define top 30, as oriented in FIG. 7. In the orientation shown in FIG. 7, the outer perimeter of plate 16 and ring 20 are thus concentric about a vertical axis X passing through the center of shield 10. The various substantially circular portions of transmission wall 18 are also substantially concentric about axis X with exceptions noted further below. When assembled, shield 10 defines an interior chamber 34 in which internal components 14 are disposed.

Top 30 and bottom 32 define therebetween a height H1 (FIG. 7) which defines the profile of shield 10 or the approximate maximum normal distance which shield 10 will extend outwardly from the surface of a support structure such as support structure 12 when mounted thereon. This distance or height H1 is generally kept to a minimum in order to minimize its interference with personnel or equipment within the area in which the shield is mounted as well as to help minimize the effect of blast waves or the impact of objects which may hit wall 18 during an explosion, structural collapse or the like.

With primary reference to FIGS. 1, 2 and 7, base plate 16 is described in greater detail. Plate 16 is in the exemplary embodiment a substantially circular rigid disc typically formed of metal and having a flat circular top surface 36, a parallel flat circular bottom surface 38 and a circular outer perimeter 40 extending therebetween. When shield 10 is in the upright position shown in FIG. 7, surfaces 36 and 38 are substantially horizontal and bottom surface 38 defines bottom 32 of shield 10. A plurality of elongated mounting through holes 42 are formed in plate 16 adjacent outer perimeter 40 and extend from top surface 36 to bottom surface 38. In the exemplary embodiment, there are eight mounting holes 42 each of which receives therethrough a mounting fastener 44 which may be in the form of a bolt, screw or any other suitable fastener depending on the nature of the support structure 12 on which shield 10 is to be mounted. Holes 42 are circumferentially equally spaced from one another and circumferentially elongated to provide for some adjustability during the mounting of shield 10 on support structure 12 to accommodate for holes in structure 12 which may be difficult to accurately form therein. A plurality of threaded holes 46 is also formed in plate 16 extending from top surface 36 toward bottom surface 38. In the exemplary embodiment, there are sixteen threaded holes 46 lying along a common circle which is disposed radially inwardly of the circle along which mounting holes 42 lie. Each of these circles is concentric about axis X when shield 10 is assembled. Fasteners 22 are typically in the form of bolts having externally threaded shafts which respectively are screwed into threaded holes 46 so that each fastener 22 provides a threaded engagement with plate 16 within each respective hole 46 to secure ring 20 and wall 18 to plate 16. Additional threaded mounting holes (not shown) may be formed radially inwardly of holes 46 for securing internal components 14 to plate 16. However, these holes would be blind holes extending from top surface 36 toward bottom surface 38 without communication with bottom surface 38.

With primary reference to FIGS. 1, 3 and 7, transmission wall 18, which is substantially circular as viewed from above, is now described in greater detail. As previously noted, wall 18 is generally dome shaped or bowl shaped and generally concentric about axis X when shield 10 is assembled. In accordance with the invention, transmission wall 18 is formed of a blast resistant and radio frequency permeable material, which may also be described as having high electromagnetic transparency. The use of such material allows for the transmission of wireless signals such as radio frequency (RF) signals therethrough while also providing a substantial blast resistance primarily to protect internal components 14 from blast waves or solid objects which may serve as projectiles during explosions or structural collapses such as that which may be experienced in an underground mine or otherwise as noted above. Typically, wall 18 is formed of a suitable plastic material which provides these properties. In the exemplary embodiment, wall 18 is formed of a polycarbonate resin thermoplastic which provides substantial strength and impact resistance, such as the polycarbonate sold under the name LEXAN®.

Wall 18 includes an annular flange 48 which in the exemplary embodiment is substantially circular and horizontally flat. Flange 48 is substantially concentric about axis X when shield 10 is assembled. Wall 18 further includes an annular side wall 50 which is rigidly secured to and extends upwardly from the inner perimeter of annular flange 48 to a substantially flat horizontal and circular top wall 52 which is rigidly secured to the top of side wall 50 and extends radially inwardly therefrom. Sixteen through holes 54 are formed in annular flange 48 extending from a flat horizontal bottom surface 56 thereof to a flat horizontal top surface 58 thereof. Holes 54 are circumferentially spaced in the same manner as threaded holes 46 and plate 16 so as to be vertically aligned therewith for receiving therethrough respective fasteners 22 when shield 10 is assembled. Bottom surface 56 has an annular configuration which is circular in the exemplary embodiment and which is also flat and horizontal. Bottom surface 56 serves as a flame-arresting or fire-arresting path surface which in the exemplary embodiment is finished to about 250 micro inches. Annular flange 48 has circular inner and outer perimeters 60 and 62 which intersect bottom surface 56 and are concentric about axis X when shield 10 is assembled. Inner and outer perimeters 60 and 62 at their intersections with bottom surface 56 define therebetween a distance D1 (FIGS. 3 and 8) which is the shortest distance therebetween as measured along bottom surface 56 and which in the exemplary embodiment is the distance between inner and outer perimeter 60 and 62 as measured along the intersection between bottom surface 56 and a vertical plane in which axis X lies when shield 10 is assembled. Distance D1 may also be described as being normal to a tangent to inner perimeter 60 or outer perimeter of 62. In the exemplary embodiment, flange 48 includes an upper ring 64 and a lower ring 66 which is rigidly and non-removably secured at its upper surface to the lower surface of ring 64 in order to add to the thickness of flange 48. Depending on the specific requirements, the use of lower ring 66 may be eliminated. In the exemplary embodiment, lower ring 66 defines bottom surface 56. If lower ring 66 is not used, then the lower surface of upper ring 64 serves as the flat horizontal bottom surface to provide the fire-arresting path surface of flange 48.

FIGS. 3 and 8 also illustrate a distance D2 which is the shortest distance along the fire arresting path surface 56 of flange 48 between inner perimeter 60 and a given one of holes 54. Distance D2 in the exemplary embodiment is the distance between inner perimeter 60 and the closest portion of hole 54 as measured along the intersection between bottom surface 56 and a vertical plane in which axis X lies when shield 10 is assembled. In addition, distance D2 in the exemplary embodiment is normal to a tangent of inner perimeter 60.

Annular side wall 50 is substantially circular as viewed from above and tapers upwardly and radially inwardly from its circular annular connection to the inner perimeter of flange 48 to its circular annular connection to the outer perimeter of circular top wall 52. Side wall 50 has a generally frustoconical configuration and has an inner surface 68 which communicates with inner perimeter 60 and an outer surface 70 which communicates with top surface 58 of flange 48. Inner surface 68 faces generally radially inwardly and downwardly while outer surface 70 faces generally radially outwardly and upwardly. Side wall 50 includes an annular lower side wall section 72 connected to and extending upwardly from the inner perimeter of flange 48, and an annular upper side wall section 74 connected to and extending upwardly from lower section 72 to the circular outer perimeter of top wall 52. In the exemplary embodiment, the sectional view of sidewall 50 illustrated in FIG. 7 shows that as viewed from the side, outer surface 70 along lower section 72 is concavely curved while inner surface 68 along lower section 72 in convexly curved. As also viewed from the side, outer surface 70 along upper section 74 is convexly curved while inner surface 68 along upper section 74 is concavely curved. Annular side wall 50 in cross section thus has a gently curving and generally open S-shaped configuration which extends from the outer perimeter of top wall 52 to the inner perimeter of flange 48 along the intersection with a vertical plane in which axis X lies. Inner surface 68 as viewed from below (FIG. 3) is generally circular and concavely curved while outer surface 70 as viewed from above is generally circular and convexly curved.

Annular side wall 50 includes a pair of generally triangular flats or flat sections 71 configured for mounting thereon respective gland seals 24A and 24B. Each section 71 includes a generally triangular flat inner surface 73 and a substantially matching generally triangular outer surface 75 which is parallel to inner surface 73. Each section 71 tapers upwardly at a constant angle from adjacent the inner perimeter of flange 48 to the outer perimeter of top wall 52. A cable-receiving through hole 77 is formed generally centrally in section 71 extending from inner surface 73 to outer surface 75 to provide communication between interior chamber 34 and atmosphere external to shield 10 when assembled. Four mounting through holes 79 are likewise formed through each section 71 and spaced outwardly from hole 77 which is positioned at the center of holes 79.

Top wall 52 in the exemplary embodiment is a flat horizontal circular disc having a flat horizontal upwardly facing top outer surface 76 and a flat horizontal downwardly facing bottom inner surface 78 which is parallel to surface 76. Top and bottom surfaces 76 and 78 define therebetween a thickness of top wall 52 which is substantially the same as the thickness of side wall 50 as defined between inner and outer surfaces 68 and 70 thereof and typically slightly less than the thickness of upper ring 64 of flange 48 although this may vary. In the exemplary embodiment, transmission wall 18 is formed by blow molding or vacuum molding such that side wall 50 and top wall 52 are thinned somewhat during the formation process while upper ring 64 substantially retains its original thickness. Inner surfaces 78 and 68 and inner perimeter 60 define therewithin a downwardly opening bowl-shaped cavity 80. Cavity 80 thus has a bottom entrance opening 81 which is completely covered by plate 16 when shield 10 is assembled. Entrance opening 81 is at the bottom or lowermost portion of transmission wall 18 and is in the exemplary embodiment the widest or largest diameter portion of cavity 80, which is thus defined by the lowermost portion of inner surface 68 or inner diameter 60. When lower ring 66 is used, inner perimeter 60 thus serves as the lowermost portion of the inner surface of transmission wall 18. The volume of cavity 80 is substantially the same as that of interior chamber 34 when shield 10 is assembled inasmuch as interior chamber 34 is defined between the flat top surface 36 of plate 16 and the inner perimeter 60 and inner surfaces 68 and 78 of transmission wall 18.

As shown in FIG. 7, wall 18 has a height H2 which is the normal distance defined between bottom surface 56 and top surface 76. Height H2 is preferably kept to a minimum in keeping with the desire to minimize the total profile of shield 10, which is represented by height H1 as previously discussed. FIG. 7 also shows that annular wall 50 has a maximum diameter D3 measured at its base, which is substantially the same as the diameter of inner perimeter 60. Generally speaking, diameter D3 is substantially greater than height H2 and in the exemplary embodiment, the ratio of diameter D3 to height H2 is on the order of about 5:1 and often falls within the range of about 4.5:1 to 5.5:1. Generally speaking, this ratio is preferably at least 4:1 or 4.5:1. The relatively minimal profile of wall 18 in combination with its overall shape substantially aids in its ability to deflect blast waves or projectiles from an external explosion or the like. More particularly, the overall circular configuration of wall 18 aids in this deflecting ability. In addition, the configuration of annular side wall 50 also aids in this deflecting ability.

Referring now to FIGS. 1, 4 and 7, retaining ring 20 is described in greater detail. Ring 20 is a substantially flat annular wall having flat circular top and bottom surfaces 82 and 84 which are parallel to one another and horizontal. Ring 20 further includes circular inner and outer perimeters 86 and 88 with sixteen through holes 90 formed therein extending from top surface 82 to bottom surface 84. Holes 90 are circumferentially evenly spaced from one another so that they align with holes 54 in flange 48 and holes 46 in plate 16 to receive therethrough respective fasteners 22 when shield 10 is assembled. Ring 20 in the exemplary embodiment is formed of a rigid material which is typically a metal such as steel or the like although ring 20 by itself may be somewhat flexible or easily bent due to the fact that it is typically relatively thin. Ring 20 helps to provide an even dispersion of the force applied by the heads of fasteners 22 when they are screwed into threaded holes 46 so that bottom surface 56 of annular flange 48 forms at atmospheric pressure a substantially airtight and water tight seal against the mating flat annular portion of top surface 36 of plate 16. Shield 10 is configured to withstand without breaking an internal pressure of at least 50 pounds per square inch (psi) within interior chamber 34, although this specification may vary depending on specific requirements. Preferably, the internal pressure which shield 10 is configured to withstand without breaking is, for instance, at least 60, 70, 80, 90, 100, 110, 120, 130 140 or 150 psi within interior chamber 34. Ring 20 helps minimize the flexing of wall 18 during an internal explosion and helps prevent flames or the like from escaping shield 10 to prevent ignition of external gasses or other materials.

Shield 10 is shown in its assembled configuration in FIG. 7, which illustrates that the threaded fasteners 22 are tightened to provide a secure threaded engagement within the corresponding threaded holes 46 of plate 16 in order to provide at atmospheric pressure the substantially airtight and water tight seal between bottom surface 56 of flange 48 and the corresponding annular circular portion of top surface 36 which engages bottom surface 56. In the exemplary embodiment, this seal is formed by the direct contact between bottom surface 56 and top surface 36. This seal can in certain circumstances be formed with the use of an O-ring which is made of rubber or an elastomer for instance, or with the use of gaskets or sealing compounds. However, some regulations may not allow for the use of these types of configurations. For instance, the Mine Safety and Health Administration (MSHA) does not allow the use of gaskets or sealing compounds in the formation of such seals. It is noted that shield 10 is configured to meet all applicable MSHA requirements although this may vary depending on the specific circumstances in which shield 10 may be used. Depending on the circumstances, it may be required that distance D1 and distance D2 meet at least a minimum value, which is true in the case of the MSHA requirements for example. More particularly, the interface between bottom surface 56 and top surface 36 between inner perimeter 60 and the closest portion of each hole 46 is a continuous mating interface between two surfaces which are sufficiently smooth and held against one another tightly enough to provide a fire arresting or fire resistant path with a minimum distance D2. Likewise, the interface between bottom surface 56 and top surface 36 extending between inner and outer perimeters 60 and 62 should be a continuous interface between mating surfaces which are sufficiently smooth and held together tightly enough to provide a fire resistant path of a minimum distance D1. These fire resistant paths thus normally extend along part of or all of the substantially airtight and water tight seal previously discussed. In the exemplary embodiment, all of the fire resistant path surfaces which form any of the fire resistant paths noted herein are finished to about 250 micro inches although this may vary depending on the requirements and materials used.

With primary reference to FIGS. 5 and 9, each gland seal 24 is described in greater detail. Each gland seal 24 includes a housing 92 which houses a compressible gland 94 and a pair of bushings 95 on opposed ends of the gland. Each gland seal also includes a hollow gland nut or follower 96, an interior mounting back plate 98, and four fasteners 100 which in the exemplary embodiment include a bolt 102, a nut 104 threadedly secured to bolt 102 along with a pair of flat washers 106 and a lock washer 108. With primary reference to FIG. 5, housing 92 is described in greater detail. Housing 92 includes a substantially flat square mounting plate 110 and a cylinder 112 which is rigidly secured along its base to mounting plate 110 via an annular weld 114. Square plate 110 has substantially flat and parallel upper and lower surfaces 116 and 118. Four mounting through holes 120 are formed through plate 110 adjacent its corners extending from upper surface 116 to lower surface 118 for receiving therethrough the threaded shafts of bolts 102. A pair of lock wire tabs 122 are secured to and extend upwardly from upper surface 116 of plate 110 on opposite sides of cylinder 112 and define through holes 124 therein for receiving a lock wire (not shown) for securing nut 96 in place as noted further below. Cylinder 112 defines an interior chamber 126 having an upper portion defined by an upper threaded section 128 of cylinder 112 and a lower gland chamber defined by a lower non-threaded portion 130 of cylinder 112. A cable-receiving through hole 132 (FIG. 9) is formed in the center of plate 110 and communicates with the gland chamber for receiving therethrough a portion of one of cables 26 or 28.

Gland nut 96 includes a hexagonal head 134 and an externally threaded portion 136 connected thereto. Head 134 may be engaged by a wrench or the like for rotatably tightening and loosening nut 96 via the threaded engagement between threaded portion 136 and the internal threaded portion 128 of cylinder 112. A through passage is formed through nut 96 which communicates with the gland chamber and atmosphere external to shield 10 whereby one of cables 26 and 28 is inserted through said passage as well as through gland 94, bushings 95, the gland chamber, hole 132, hole 77, and a central cable receiving hole 140 formed in the center of back plate 98 whereby said cable 26 or 28 extends from outside shield 10 to inside shield 10 within interior chamber 34. Like mounting plate 110, back plate 98 includes four mounting holes 142 extending therethrough for receiving the threaded shafts of bolts 102 so that the threaded engagement of bolts 102 and nuts 104 secures the respective gland seal 24 on transmission wall 18 with mounting section 71 clamped or sandwiched between mounting plates 98 and 110 under suitable pressure to provide at atmospheric pressure a gas or airtight and water tight seal therebetween. A lock wire hole 138 is formed through head 134 of nut 96 such that hole 138 and holes 124 in the lock tabs 122 may receive a wire threaded therethrough to secure nut 96 in place when it is in a tightened position to prevent nut 96 from loosening. FIG. 9 shows the mounting of one of cables 26 and 28 as nut 96 is rotated to thread the nut into the cylinder and compress gland 94 in the direction shown by arrow A in FIG. 9 such that gland 94 applies radially outward force against the inner surface of cylinder 112 and radially inward force against the outer surface of the cable 26 or 28 in order to secure the cable and provide at atmospheric pressure substantially a gas or airtight, water tight seal between gland 94 and each of the inner surface of cylinder 112 and the outer surface of the cable.

There are additional fire resistant paths illustrated in FIGS. 9 and 9A having respective minimum distances D4, D5 and D6. More particularly, bottom surface 118 of mounting plate 110 and outer surface 75 of mounting section 71 form a continuous mating interface between the edges of holes 132 or 77 and the closest part of the outer perimeter of plate 10 where it intersects with bottom surface 118 so that this interface provides a fire resistant path having a minimum distance D4 wherein the continuous interface typically provides at atmospheric pressure an airtight and water tight seal between surfaces 118 and 75. FIG. 9A illustrates a similar continuous interface serving as a fire resistant path between bottom surface 118 and top surface 75 wherein this fire resistant path extends the shortest distance between the edge of hole 77 and the edge of one of holes 79, or between the edge of hole 132 and the edge of one of holes 120, such that this fire resistant path has a minimum distance D5. FIG. 9A also illustrates a fire resistant path which is the continuous interface between the outer surface of cable 26 or 28 and the inner perimeter of gland 94 and is measured in the direction of the length of the cable. This fire resistant path has a minimum distance D6. Similarly, FIG. 9A illustrates an additional fire resistant path between the inner surface of non-threaded portion 130 of cylinder 112 and the outer perimeter surface of gland 94 as measured in the direction in which the cable is elongated in the region of gland 94. This fire resistant path also has a minimum distance D6. Each of distances D4, D5 and D6 typically equal or exceed the MSHA minimum requirements for such fire resistant paths.

As previously noted, blast shield 10 in the exemplary embodiment is configured to meet or exceed all of the MSHA requirements with regard to explosion-proof enclosures. Some of these requirements or standards will now be discussed in greater detail. For example, transmission wall 18 is configured to undergo without breaking an impact test in accordance with ASTP 2132 Version 2008-03-26 of the MSHA Approval and Certification Center, the title of which is “Lens Impact Test 18.66(a)”, which is incorporated herein by reference in its entirety. This test is typically conducted while the shield 10 is assembled. However, transmission wall 18 is configured to pass this test as a stand alone component. The impact test requires that the center of the lens is to be the point of impact, which in this case is the center of top wall 52, which is illustrated at axis X in FIG. 6. The test is more particularly formed using a drop weight test apparatus which is shown and described in ASTP 2132. The test apparatus includes a four pound weight, the bottom of which includes a one inch hemispherical striking surface which is used to strike the center of the lens when dropped. A height adjustment mechanism such as a height adjustment screw is used to control the height from which the weight is dropped during the test. The drop distance is defined as the distance (prior to dropping the weight) between the striking surface of the drop weight and the top of the accessory, namely the center of the lens which in the present case is the center of top wall 52 when positioned horizontally. For round windows or lenses, the height of the fall or distance that the drop weight is to be dropped varies depending of the diameter of the lens. For a lens having a diameter of one inch to less than four inches, the height of fall is six inches; where the diameter is greater than or equal to four inches and less than five inches, the height of fall is nine inches; when the diameter is greater than or equal to five inches and less than six inches, the height of fall is fifteen inches; and when the diameter is equal to or greater than six inches, the height of fall is twenty-four inches. ASTP 2132 also provides the height of fall for windows or lenses which are irregularly shaped, although those are not stated here for brevity.

In addition, transmission wall 18 is configured to undergo without breaking or other defined defect a thermal shock test in accordance with ASTP 2131 Version 2008-04-23 of the MSHA Approval and Certification Center, which is a thermal shock test on windows or lenses, which is incorporated herein by reference in its entirety. This test is conducted with the shield 10 in assembled form although transmission wall 18 is also configured to pass this test as a stand alone component. In order to pass this thermal shock test, ASTP 2131 requires that the lens after the test may not have any defects greater than as defined in ACRI 2102. To that effect, ACRI 2102 Version 2008-11-26 of the MSHA Approval and Certification Center, having a title of “Criteria for the Evaluation Of A Window Or Lens Used As Part Of An Explosion-Proof Enclosure”, is incorporated herein by reference in its entirety. ASTP 2131 indicates that a defect shall be defined as a crack, chip, break, flaw, fracture, warpage or crazing observed on the sample or assembly, thus namely the transmission wall 18 or shield 10. ACRI 2102 provides the definition of a crack as being a separation of material throughout its thickness; and the definition of craze as defects that appear as surface cracks and have a silvery appearance when light is passed through the material. An abbreviated description of the thermal shock test of ASTP 2131 is now described. In short, the thermal shock test involves the heating of the lens to a certain temperature and the immersing of the lens into water at a lower temperature. A drum or tank of water is provided which is of a sufficient size in order to allow the entire sample to be immersed, namely the entire shield 10 where tested as assembled. The volume of the water is also to be sufficient to cool the sample without raising the temperature of the water by more than 5° C. To perform the test, the shield is heated in an oven so that the temperature of the lens or transmission wall reaches 115° C. (240° F.) for a polycarbonate lens or 150° C. (302° F.) for a glass lens. The water in the tank is to be between 15° C. (59° F.) and 20° C. (68° F.) prior to immersing the heated sample. Once the temperature of the lens has stabilized for a period of fifteen minutes, the sample is removed from the oven and immediately immersed in the cooler water and allowed to cool to the temperature of the water. The sample is then removed from the water and inspected for visual defects such as breakage or the other defects noted above.

Furthermore, blast shield 10 is configured to pass the test as described in ASTP 2137 Version 2005-11-08 of the MSHA Approval and Certification Center, having a title of “Requirements For Explosion Testing Per 30 CFR 18.62”, which is incorporated herein by reference in its entirety. In short, this test creates an internal explosion within the interior chamber of the enclosure or blast shield 10 under specific circumstances while the shield is disposed within a gallery or explosion test chamber. In short, the explosion-proof container or blast shield 10 is positioned within an explosion test gallery or chamber with the enclosure and test chamber filled with an explosive mixture, and a single spark plug is positioned in order to ignite the explosive mixture within the enclosure such as blast shield 10 to determine if the enclosure meets various requirements.

In order to fully meet the requirements of ASTP 2137, the enclosure must undergo a minimum of sixteen of such tests. Blast shield 10 is configured to undergo these sixteen tests and pass all of the various criteria required by ASTP 2137. Thus, blast shield 10 is likewise capable of undergoing any lesser number of these tests, that is, any number from one to fifteen of the tests, while passing any number of the criteria required by ASTP 2137. The test more particularly requires that the enclosure is filled with and surrounded by an explosive mixture of natural gas and air or methane and air. If natural gas is used, the content of methane and ethane shall total at least 98% by volume with nitrogen and propane the remainder. The internal mixture within the enclosure is ignited by an electrical spark of 100 millijoules or greater. ASTP 2137 describes the various tests in much greater detail, including several variables which are used to meet the full requirements of the explosion test. ASTP 2137 even requires that the test must be conducted under conditions most likely to result in test failure, such as 9.6% CH4 (methane) gas-air mixture, optimum spark location and testing with and without dummies, which are defined as parts substituted during explosion testing for internal electrical components. Some of the tests also include placing coal dust within the enclosure prior to ignition. The passing criteria or acceptable performance for the tested explosion-proof enclosure is, as a result of the ignition and internal explosion within the enclosure, no discharge of flame from the enclosure; no ignition of the explosive mixture in the gallery or explosion test chamber; no development of after burning, which is defined as the combustion of a flammable mixture that is drawn into an enclosure after an internal explosion has occurred; no rupture of any part of the enclosure; no permanent distortion of any planar surface of the enclosure exceeding 0.040 inch per linear foot; no excessive clearances along flame-arresting paths following retightening of fastenings, as required; no pressure exceeding 125 psi, unless the enclosure has withstood a static pressure of twice the highest value recorded in the test; and no looseness or physical damage to a window or lens.

Shield 10 is also configured to meet certain ingress protection standards, such as those set forth by the International Electrical Commission (IEC), that is, protection against the ingress or entry of solid objects and liquids into an enclosure. Shield 10 is configured to have at least an IP 66 rating or IP 67 rating in accordance with IEC Publication 60529 (IEC 60529), which is incorporated herein by reference. In the rating, IP stands for ingress protection, the first number indicates the level of protection against ingress of solid objects, and the second number indicates the level of protection against ingress of liquids. The IP 66 rating thus specifies that blast shield 10 is dust tight or totally protected against dust, and is protected against powerful jets of water from any direction. The IP 67 rating specifies that blast shield 10 is dust tight or totally protected against dust, and is protected against temporary immersion in water at a depth between 15 cm and 1 meter. This rating system, or rating itself, is sometimes referred to as the IP Code, International Protection Rating or Ingress

Protection Rating. Under IEC 60529, the first number ratings basically mean the following: 0=no special protection; 1=protected against solid objects 50 mm or greater; 2=protected against solid objects 12 mm or greater; 3=protected against solid objects 2.5 mm or greater; 4=protected against solid objects 1 mm or greater; 5=protected against dust (no harmful deposit); and 6=totally protected against dust. Under IEC 60529, the second number ratings basically mean the following: 0=not protected; 1=protected against vertically dripping water; 2=protected against vertical dripping water when enclosure is tilted up to 15° from the vertical; 3=protected against direct sprays of water up to 60° from the vertical; 4=protected against splashing water from any direction; 5=protected against low pressure jets of water from any direction; 6=protected against powerful jets of water from any direction (temporary flooding of water, e.g. for use on ship decks against heavy seas); 7=protected against temporary immersion in water at a depth between 15 cm and 1 meter; and 8=protected against continuous or long periods of immersion at a depth greater than 1 meter. Blast shield shield 10 is thus obviously also protected at all of the IP ratings less than IP 66.

IP ratings sometimes include a third number, from earlier versions of IEC 60529, which related to resistance to mechanical impact, which was identified as energy measured in joules which the impacted enclosure could withstand without breaking. There is also a newer IK number or rating which is in many cases now used in place of the earlier specifications. The IK number is specified in IEC 62262 or European standard EN 62262 (formerly known as EN 50102), each of which is incorporated herein by reference. These impact tests are generally similar to the MSHA impact test discussed further above. Using one of these impact tests, transmission wall 18 is configured to undergo or withstand without breaking an impact energy of at least 5 joules, which is equivalent to an impact from dropping a 1.7 kg (3.3 lbs.) weight from a height of 29.5 cm (15.75 inch), or 6 joules, which is equivalent to an impact from dropping a 1.5 kg (3.75 lbs.) weight from a height of 40 cm (11.6 inch).

FIG. 10 illustrates an alternate gland seal 146 which may be used with an alternate transmission wall 18A. This arrangement would typically be used when the requirements regarding the flame path are less stringent than those associated with the use of gland seal 24. Alternate transmission wall 18A is very similar to wall 18 except that it includes one or more mounting sections 71A which are analagous to mounting sections of 71 but have only a single cable receiving hole 77A formed therethrough without the use of mounting holes corresponding to mounting holes 79 of the mounting section 71 of wall 18. Hole 77A is typically somewhat larger than hole 77 to accommodate the alternate gland seal 146. Gland seal 146 includes an externally threaded tube 148 which extends through hole 77A, an internally threaded gland nut 150 which threadedly engages one end of tube 148, and a gland 152 which is disposed within a gland chamber formed within gland nut 150. An outside mounting nut 154 and an inside mounting nut 156 are threaded onto externally threaded tube 148 so that outside nut 154 engages the outer surface of mounting section 71A and inside nut 156 engages the inner surface of mounting section 71A in order to secure gland seal 146 to mounting section 71A. The basic operation of gland seal 146 is similar to that of gland seal 24 in that the tightening of gland nut 150 on tube 148 compresses the gland 152 in order to provide at atmospheric pressure the gas or airtight and water tight seal between the gland, the cable and inner surface of nut 150. Cable 26 or 28 thus passes through tube 148 and gland nut 150 to extend from outside the blast shield to inside its interior chamber.

With reference to FIG. 11, a wireless transmission system in which shields 10 are used is now described. There are a number of operational environments in which the wireless transmission system utilizing shields 10 may be typically used. FIG. 11 is a diagrammatic view illustrating the operational environment as being an underground mine 160. However, the system may be used in other underground environments such as a subway. In addition, the system is suited for use in various industries (typically above ground), especially within large plants in which wireless mesh networks are particularly desirable. Wireless mesh networks are advantageous in one regard in that they eliminate a large amount of electrical wiring or other signal transmission lines which would otherwise be used. The system is also configured for use in petrochemical industry or other industries which utilize volatile liquids or include flammable gasses. As previously noted, shields 10 are specifically configured to prevent any internal arcing or explosions from igniting such flammable gasses external to the shield. Other industries which utilize highly flammable materials such as gun powder or fine dust particles which could easily be ignited may also be served well with the present system.

With continued reference to FIG. 11, mine 160 includes a mine shaft which may branch as shown and include a mine portal or entrance 162 or multiple entrances. As is well known in the mining industry, some underground mines are very extensive and may extend for miles in various directions with multiple branches. FIG. 11 further shows an electric power source 164 with electric power lines 166 in electrical communication with power source 164 and power cables 26 of several blast shields 10. As previously noted, the battery of the internal components 14 is kept charged via its charger by this connection to power source 164. As shown in FIG. 11, some of the shields are marked 10A and others 10B. The ones marked 10A utilize power cable 26, but do not utilize the signal transmission cable 28. Thus, blast shields 10A may be formed without cable 28, gland seal 24B and the associated mounting section 71 shown in the previous figures. On the other hand, the shields which are generally closer to entrance 162 are marked as shields 10B and include the transmission cable 28 in addition to the power cable 26. The system further includes communication lines 168 which are in communication with transmission cables 28 and also with an information receiving unit which is external to the mine. Unit 170 may represent a variety of devices which typically include some sort of processing unit for translating data received via lines 168 into information which may, for example, be tracked by a computer or viewed on a screen. Unit 170 may thus include a computer for running a suitable program for processing or translating information received thereby.

FIG. 11 also shows several inertial sensor units 172 having antennas 174. One of units 172 is shown at a battery charging and reset station 176 which is in electrical communication with power source 164. Each inertial sensor unit 172 typically includes a housing containing a radio frequency transmitter, an inertial sensor, a micro processor and a battery for powering the unit. The inertial sensor during movement produces velocity data which the micro processor translates into a signal which is transmitted by the transmitter via antenna 174 to any of the receivers which are housed within blast shields 10 within the transmission range of the given unit 172. Shields 10 are typically spaced 500 to 1000 feet apart from one another and thus serve as nodes or relays for receiving transmissions either from unit 172 or from another transmitter within a different shield 10 and relaying the signal via its transmitter to any other receivers within its transmission range. Radio frequency signals may thus be transmitted from outside to inside the blast shield to be received by the internal receiver as well as transmitted from the internal transmitter from inside to outside the blast shield through transmission wall 18 due to the fact that it is formed of a material which is sufficiently permeable to radio frequency or sufficiently electromagnetically transparent to allow for the radio waves to pass therethrough. Although unit 172 may include an inertial sensor as noted, it may also include devices other than inertial sensors for producing signals to be transmitted to the relay stations provided within each shield 10. Inertial sensor units 172 may be positioned at charging and reset station 176 in order to charge the onboard battery as well as to set or reset the alignment of the inertial sensor to a home position. In the underground mine setting, this setting or resetting process is typically accomplished utilizing a pair of underground geodetic survey monuments. The specific use of such an underground inertial sensor tracking system is described in greater detail in U.S. Pat. No. 7,400,246 granted to Breeding, which is incorporated herein by reference. Inertial sensor units 172 may be hand held units which can be carried by hand by miners or other personnel and or they may be carried by an individual by, for example, securing unit 172 to a belt which can be worn by an individual or some other type of body wearable pack. Units 172 may also be mounted on mining machinery or other mobile machines for tracking their movement.

As noted above, unit 172 may utilize a transmitter without the use of an inertial sensor, and thus unit 172 also represents more broadly a transmitter unit which may be configured to transmit signals related to any kind of information or data packets with which the wireless transmission system of the invention may be used. One feasible use for the present system relates to life cycle monitors which may be used on various types of machines for the purpose of tracking or monitoring the life of a given machine in order to ascertain when the machine needs to be repaired or replaced. For example, vibration sensors or temperature sensors may be mounted on or near such a machine in order to monitor the machine's vibrations and temperature, which can provide pertinent information as to what stage the machine is in its life cycle. Such sensors may produce signals which can be wirelessly transmitted via the electric mesh network of the present invention to a computer or the like at a remote location as generally indicated at 170 in FIG. 11. The signals from the life cycle sensors or the like may enter the wireless mesh network initially either via a wireless transmission or via transmission lines. For instance, a machine's life cycle sensor may be in communication with its own transmitter which transmits wireless signals to a receiver within one of shields 10 for retransmission via the transmitter within the shield. Such life cycle sensors could also be wired via transmission lines such as lines 28 to transmit the signal via the transmission line into the interior chamber of the shield so that the internal transmitter thereof would itself begin the wireless transmissions within the network. The present invention may also be useful in process control such that various types of sensors could similarly produce signals which could be transmitted over the wireless mesh network to, for example, a remote controller such as indicated generally at 170 which would control a device associated with the process control sensors in accordance with the signals received therefrom. Controller 170 could thus provide return signals over the wireless mesh network so that the transmitted signal would control the given device. This would allow for the remote control of various types of machines or devices within a large manufacturing plant, for example.

Blast shield 10 thus provides an enclosure for housing various electronic components including a wireless transmitter so that a wireless mesh network may be used in various environments. For instance, shield 10 provides a blast resistant or blast proof enclosure for protecting the internal electronic components from blast waves or shock waves or various materials which may impact the shield during explosions or the collapse of a mine or other structure. Shield 10 also provides a gas tight enclosure with suitable fire resistant or fire arresting paths to prevent the escape of flames or electrical sparks from inside the shield which could otherwise ignite flammable materials external to the enclosure. In addition, shield 10 provides a dust proof and water proof or water resistant enclosure which thus protects the internal components from dusty and moist environments.

In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed.

Moreover, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described. 

1. A blast shield comprising: a blast resistant housing; an interior chamber formed in the housing and substantially sealed from atmosphere external to the housing; and a transmission wall of the housing formed of a material through which a wireless signal is transmittable from inside the interior chamber to outside the housing.
 2. The blast shield of claim 1 wherein the transmission wall comprises an annular sidewall.
 3. The blast shield of claim 2 wherein the annular sidewall tapers upwardly and radially inwardly.
 4. The blast shield of claim 3 wherein the transmission wall comprises an annular flange extending radially outwardly from the annular sidewall; and the annular sidewall tapers upwardly and radially inwardly from adjacent the annular flange.
 5. The blast shield of claim 4 wherein the transmission wall comprises a top wall extending radially inward from the annular sidewall; and the annular sidewall tapers upwardly and radially inwardly from adjacent the annular flange to adjacent the top wall.
 6. The blast shield of claim 2 wherein the annular sidewall comprises an annular lower sidewall section and an annular upper sidewall section connected to and extending upwardly from the lower sidewall section; the lower sidewall section has an outer surface which is concavely curved as viewed from the side; and the upper sidewall section has an outer surface which is convexly curved as viewed from the side.
 7. The blast shield of claim 2 wherein the transmission wall comprises an annular flange extending radially outwardly from the annular sidewall; and the annular sidewall extends upwardly from the annular flange.
 8. The blast shield of claim 7 wherein the transmission wall comprises a top wall extending radially inward from the annular sidewall.
 9. The blast shield of claim 1 wherein the transmission wall has a bowl-shaped configuration.
 10. The blast shield of claim 1 further comprising a retaining ring; an annular flange of the transmission wall; and a base of the housing; and wherein the flange is clamped between the retaining ring and the base.
 11. The blast shield of claim 1 further comprising a wireless transmitter in the interior chamber.
 12. The blast shield of claim 11 further comprising a cavity defined by the transmission wall; and wherein the transmitter is within the cavity.
 13. The blast shield of claim 1 further comprising a through hole formed in the transmission wall; and a cable which extends from outside the transmission wall through the hole into the interior chamber.
 14. The blast shield of claim 13 further comprising a gland seal around the cable adjacent the transmission wall.
 15. The blast shield of claim 14 further comprising an internal plate; an external plate; a gland seal housing secured to one of the plates; and a portion of the transmission wall clamped between the plates.
 16. The blast shield of claim 1 further comprising a first component of the housing; a first fire-arresting surface on the first component; a second component of the housing; a second fire-arresting surface on the second component; an interface between the first and second fire-arresting surfaces to provide a fire resistant path configured to prevent electrical arcing or an explosion within the interior chamber from exiting the housing so as to present a danger of igniting flammable material external to the housing.
 17. The blast shield of claim 1 wherein the housing is configured to withstand an internal pressure of at least 50 pounds per square inch within the interior chamber without breakage of the housing.
 18. The blast shield of claim 1 wherein the housing has at least an IP 66 rating in accordance with IEC Publication
 60529. 19. The blast shield of claim 1 wherein the transmission wall is configured to undergo without breaking one of (a) an impact energy of at least 5 joules; (b) an impact test in accordance with ASTP 2132 Version 2008-03-26 of the Mine Safety and Health Administration (MSHA) Approval and Certification Center; and (c) a thermal shock test in accordance with ASTP 2131 Version 2008-04-23 of the Mine Safety and Health Administration (MSHA) Approval and Certification Center.
 20. The blast shield of claim 1 wherein the housing is configured to undergo an explosion within the interior chamber in accordance with ASTP 2137 Version 2005-11-08 of the Mine Safety and Health Administration (MSHA) Approval and Certification Center with a result selected from the group consisting of (a) no discharge of flame from within the interior chamber to atmosphere external to the housing; (b) no rupture of any part of the housing; (c) no permanent distortion of any planar surface of the housing exceeding 0.040 inch per linear foot; (d) no ignition of an explosive mixture in an explosion test chamber in which the blast shield is disposed during the explosion; and (e) no combustion of a flammable mixture that is drawn into the interior chamber after the explosion has occurred while the blast shield is disposed within an explosion test chamber filled with an explosive mixture. 